Acute uncomplicated pyelonephritis (APN) is a complex clinical entity, which is defined differently based on clinical or imaging criteria. The aim of this study was to describe the clinical and radiological presentation of APN-upper urinary tract infection (UTI) cases observed between May 2005 and June 2006 and hospitalised in the Emergency Medicine ward of San Luigi Hospital, Orbassano, Turin, Italy. All patients underwent imaging scans and were differentiated on the basis of parenchymal involvement. Of around 45 000 patient visits to the emergency room between May 2005 and June 2006, 23 patients were diagnosed as having uncomplicated upper UTI (all female, age 15–57 years). Renal parenchymal involvement was confirmed by imaging in 16 cases (69.6%). The imaging spectrum ranged from a small single lesion to large multiple defects; on admission, 2 cases had no pain and 2 had no fever; lower urinary tract symptoms were present in only 13 patients (7 with parenchymal involvement). All patients with parenchymal involvement had at least one sign of systemic inflammation-infection. Most patients (15) had taken antibiotics before hospitalisation; consequently, urine cultures were negative in 21 cases (14 cases with positive imaging (87.5%)). The data from patients with and without parenchymal involvement overlapped, the only difference being a higher prevalence of high CRP levels in cases with parenchymal involvement.